Present voltage reference circuits for use in radiation hard systems use either magnetic references or reverse biased semiconductor PN junction devices. Voltage references utilizing magnetic references are very large and sensitive to external magnetic fields. Voltage references utilizing PN junctions use fewer parts but shift much more in radiation. These junctions individually shift much more because their output is determined by a relatively low concentration of dopant atoms. As a result of neutron irradiation a large percentage of these dopant atoms are removed from the conduction band. A tunnel diode is a forward biased PN junction whose output is determined by a dopant concentration many orders of magnitude heavier than the typical reverse biased semiconductor reference. A much lower percentage of the dopant atoms is removed by radiation and the tunnel diode output changes a correspondingly much lower amount.